723 research outputs found
Dual-mode operation of a neutron source, a concept
Pulsed neutron source operates in conjunction with a photomultiplier tube coupled to a gamma ray scintillation crystal. This allows measurements of gamma radiation from both inelastic scattering and thermal neutron capture in a single experiment
Neutron die-away experiment for lunar and planetary surface analysis Final report, 26 Jul. 1966 - 26 Mar. 1967
Neutron and gamma ray die-away experiment for lunar and planetary surface analysi
Systems effectiveness evaluation program
Eight integrated computer programs provide needed capability to reduce man-hours needed to perform routine monitoring and assessment of effectiveness, reliability, and maintainability of large electronic equipment systems
Efficient decomposition of quantum gates
Optimal implementation of quantum gates is crucial for designing a quantum
computer. We consider the matrix representation of an arbitrary multiqubit
gate. By ordering the basis vectors using the Gray code, we construct the
quantum circuit which is optimal in the sense of fully controlled single-qubit
gates and yet is equivalent with the multiqubit gate. In the second step of the
optimization, superfluous control bits are eliminated, which eventually results
in a smaller total number of the elementary gates. In our scheme the number of
controlled NOT gates is which coincides with the theoretical lower
bound.Comment: 4 pages, 2 figure
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Computationally-Efficient Visual-Inertial Simultaneous Localization and Mapping for Spaceflight Navigation
This thesis represents an investigation into the application to spaceflight of the estimation techniques developed to solve the well-known robotics problem of Simultaneous Localization and Mapping (SLAM). This subject has been thoroughly studied in the context of ground and aerial robotics but its study for use in the spaceflight domain, where the dynamical, measurement, and computational challenges are often very different than in terrestrial applications, is less common. Further, the wide body of extant robotics research into SLAM can be difficult to approach and understand for space navigators with a more classical estimation background because of the differences in terminology and assumptions that roboticists have utilized over time. This work offers an overview of the development of SLAM in robotics and how it has been applied in that field, as well as an accessible approach to the problem for researchers with an aerospace background. This also leads into the development of a novel visual-inertial (VI) SLAM algorithm designed to achieve constant-time exploration and mapping while still integrating the full nonlinear dynamics of the space environment, handling the high update rates of inertial measurement units (IMUs), and incorporating the measurement information produced by a camera sensor. This algorithm is applied to 2D and 3D simulated and real datasets to demonstrate its capability to quickly generate accurate state estimates of both spacecraft and environmental variables.</p
Transmission of bovine viral diarrhea virus among white-tailed deer (Odocoileus virginianus)
Cattle persistently infected (PI) with bovine viral diarrhea virus (BVDV), a pestivirus in the family Flaviviridae, are an important source of viral transmission to susceptible hosts. Persistent BVDV infections have been identified in white-tailed deer (Odocoileus virginianus), the most abundant free-ranging ruminant in North America. As PI deer shed BVDV similarly to PI cattle, maintenance of BVDV within white-tailed deer populations may be possible. To date, intraspecific transmission of BVDV in white-tailed deer has not been evaluated, which prompted this study. Six pregnant white-tailed deer were captured in the first trimester of pregnancy and cohabitated with a PI white-tailed deer. Cohabitation with the PI deer resulted in BVDV infection in all does, as indicated by seroconversion. All does gave birth to live fawns and no reproductive losses were observed. At birth, evidence of BVDV infection was identified in two singlet fawns, of which one was determined to be PI by repeated serum reverse transcription nested PCR, whole blood virus isolation and immunohistochemistry. This study demonstrates for the first time that BVDV transmission may occur among white-tailed deer. The birth of a PI fawn through contact to a PI white-tailed deer indicates that under appropriate circumstances, BVDV may be maintained in white-tailed deer by congenital infection
Monte Carlo study of the Widom-Rowlinson fluid using cluster methods
The Widom-Rowlinson model of a fluid mixture is studied using a new cluster
algorithm that is a generalization of the invaded cluster algorithm previously
applied to Potts models. Our estimate of the critical exponents for the
two-component fluid are consistent with the Ising universality class in two and
three dimensions. We also present results for the three-component fluid.Comment: 13 pages RevTex and 2 Postscript figure
Population Genetics of Bowhead Whales (Baleana mysticetus) in the Western Arctic
Bowhead whales (Balaena mysticetus) in the Bering, Chukchi, and Beaufort seas experienced a severe reduction as a result of commercial whaling in the 19th century. Since the cessation of commercial whaling, the population has recovered to a size that is approaching pre-whaling estimates. Inupiat and Yupik communities in northern and western Alaska hunt these Western Arctic (WA) bowheads along their migratory path during spring and fall. This hunting is regulated by the International Whaling Commission. Recent but preliminary analysis of available genetic data (207 whales and 10 microsatellite markers) raised the question of the presence of multiple, genetically distinct populations within the WA bowheads. Here we re-examined this question on the basis of a study of 414 whales and 22 newly developed microsatellite loci. We identified widespread departures from Hardy-Weinberg equilibrium; however, we were unable to detect significant evidence of multiple genetic populations within the WA bowheads that could explain this Hardy-Weinberg disequilibrium, particularly when compared to the strength of evidence for differentiation between WA bowheads and other populations from distant regions such as the Okhotsk Sea and eastern Canada. There was conclusive evidence of genetic differentiation among the three regions. The statistical rejection of panmixia within the WA improves our understanding of bowhead whale biology, and the lack of evidence for multiple populations within the WA enables risk-averse management of aboriginal hunting of Western Arctic bowhead whales.La population de baleines borĂ©ales (Balaena mysticetus) des mers de BĂ©ring, de Tchoukotka et de Beaufort a enregistrĂ© un grave dĂ©clin en raison de la pĂȘche commerciale Ă la baleine au XIXe siĂšcle. Depuis que la pĂȘche commerciale Ă la baleine a cessĂ©, la population de baleines borĂ©ales a connu un certain essor au point oĂč elle approche maintenant les estimations de la taille quâelle avait avant la pĂȘche commerciale Ă la baleine. Les collectivitĂ©s Inupiat et Yupik du nord et de lâouest de lâAlaska chassent les baleines borĂ©ales de lâouest de lâArctique le long de leur voie de migration au printemps et Ă lâautomne. La chasse est rĂ©glementĂ©e par lâInternational Whaling Commission. Des analyses rĂ©centes, bien que prĂ©liminaires, des donnĂ©es gĂ©nĂ©tiques disponibles (207 baleines et 10 marqueurs microsatellites) ont soulevĂ© la question de la prĂ©sence de multiples populations gĂ©nĂ©tiquement distinctes au sein de la population de baleines borĂ©ales de lâouest de lâAlaska. Ici, nous avons rĂ©examinĂ© cette question en fonction de lâĂ©tude de 414 baleines et de 22 locis microsatellites nouvellement mis au point. Nous avons remarquĂ© dâimportantes dĂ©viations de lâĂ©quilibre de Hardy-Weinberg; toutefois, nous nâavons pas pu trouver de preuve significative de populations gĂ©nĂ©tiques multiples au sein des baleines borĂ©ales de lâouest de lâAlaska qui pourrait expliquer ce dĂ©sĂ©quilibre de Hardy-Weinberg, plus particuliĂšrement en comparaison avec la force de la preuve de diffĂ©renciation entre les baleines borĂ©ales de lâouest de lâArctique et dâautres populations de rĂ©gions distantes telles que la mer dâOkhotsk et lâest du Canada. Il y avait des preuves concluantes de diffĂ©renciation gĂ©nĂ©tique entre les trois rĂ©gions. Le rejet statistique de la panmixie au sein de lâouest de lâArctique amĂ©liore notre comprĂ©hension de la biologie des baleines borĂ©ales, et le manque de preuves de populations multiples dans lâouest de lâArctique donne lieu Ă la gestion de lâaversion au risque de la chasse Ă la baleine borĂ©ale de lâouest de lâArctique par les Autochtones
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